Thy-1+ epidermal cells in nude mice are distinct from their counterparts in thymus-bearing mice. A study of morphology, function, and T cell receptor expression

We have evaluated the morphology, function, and TCR mRNA and DNA profiles of Thy-1+ epidermal cells (EC) derived from athymic (nude) mice. Based on these criteria we demonstrate that Thy-1+ EC in nude mice are predominantly round and angular and located in follicular epithelium, as compared to predominantly dendritic, interfollicular Thy-1+ EC found in normal CBA or BALB/c mice. Functionally, Thy-1+ EC from normal mice proliferate and elaborate IL-2 in response to stimulation by Con A; by contrast, nude Thy-1+ EC fail to proliferate or secrete IL-2 in response to Con A. Nude Thy-1+ EC proliferate markedly in response to low-dose IL-2 alone; Thy-1+ EC from normal mice give only modest proliferative responses to IL-2. Both populations of cells proliferate and elaborate IL-2 in response to PMA and calcium ionophore. Short-term cultured Thy-1+ EC from nude mice resemble Thy-1+ EC from normal animals in that they express no detectable functional TCR-alpha and beta-RNA. Normal Thy-1+ EC express abundant levels of functional RNA for TCR-gamma and delta-chains and for the CD3 delta-chain, whereas nude Thy-1+ EC produce no detectable TCR-delta and no CD3 delta-RNA and only truncated, presumably germ-line TCR-gamma transcripts, as suggested by lack of hybridization with gamma-V region probes and by lack of detectable rearrangements in the gamma-genes. These phenotypic, functional, and genotypic characteristics of Thy-1+ EC from nude mice suggest that these cells are at a very early stage of T cell differentiation.